Air bags have evolved over the past few decades from driver's side air bags containing two roughly symmetrical (usually circular) bag panels to more complicated passenger side and side curtain air bags having unique geometries and configurations. Side curtain air bags generally are deployed from packing containers positioned within the roofline along the side windows of a vehicle. These side curtain bags, which are designed to protect passengers during rollover crashes by retaining the inflation state for a long duration, should not only provide cushioning effects, but also provide protection from broken glass and other debris. Therefore, it is imperative that side curtain air bags retain large amounts of gas (at high gas pressures) to remain inflated throughout the potentially long time periods associated with a rollover occurrence.
It has been found that efficient side-curtain air bags may be produced as one-piece woven (preferably Jacquard woven) articles. A one-piece Jacquard air bag cushion is more economical to produce due to the elimination of cutting and sewing steps typically associated with production of multi-panel air bags. The distinct disadvantage of this system is that the target bag must be coated on the outside during production. Whereas traditional driver-side bags included coatings on the interior of the bag components, these one-piece woven structures necessitate coatings on the exterior of the bag component (that is, coating the interior of the finished bag is not possible).
Coatings have typically been applied to fabrics for automotive air bags to resist the unwanted permeation of air through the fabric and, to a lesser extent, to protect the fabric from the hot gases used to inflate the bags. A variety of materials have been used to create these fabric coatings, ranging from early efforts in which polychloroprene was the material of choice to later efforts in which silicone or silicone-containing materials were preferred. Efforts, in which silicone polymer blends are used as air bag coatings, are described, for example, in U.S. Pat. Nos. 6,348,543; 6,468,929; and 6,545,092.
In the case of one-piece, side curtain-type air bags, having a highly functional coating is especially important. Unlike driver-side bags, coated on the interior, where excursion of the bag tends to press the coating against the fabric surface, in one-piece bags, coated on the exterior, the coating is actually pushed away from the fabric surface during deployment. This force has the potential to cause two significant problems—rupture of the coating and delamination of the coating from the bag panel—that may lead to the failure of the bag as a whole. The present disclosure provides a coating composition that overcomes these issues in effective manner that is both economically feasible and environmentally friendly.
Although silicone polymers alone have a number of shortcomings (e.g., relatively high air permeability, relatively high cost, and tendency to cause yarn shifting due to its lubricating properties), it has been found that one can modify the behavior of silicone polymers by forming what are called “interpenetrating polymer networks” (IPNs). IPNs are a special class of polymer blends in which the polymers exist in networks that are formed when the polymer components are thermodynamically compatible to a point at which they dissolve, or are essentially microscopically dispersed, in each other. Classical, or true, IPNs occur when all of the polymer species within a blend form chemical cross-links.
In previous attempts to produce IPNs, the components have been dissolved in a common solvent and, ultimately in each other (i.e., a polymer is dissolved with silicone in a solvent). Toluene is one example of such a solvent. While functional coatings have been developed in this manner, manufacturers of air bag fabrics have sought to replace solvent-based formulations with other systems that are less expensive, safer, and more environmentally friendly. The present disclosure addresses these manufacturer needs by replacing the solvent-dissolved polymeric solids of previous attempts with a polymer blend comprised of liquid silicone rubbers and liquid copolymers.